1. Field
Example embodiments relate to heat treatment apparatuses and/or methods for liquid crystal display (LCD) cells.
2. Description of the Related Art
In a stage before electronic devices such as drive modules are mounted thereto, an LCD cell has a structure in which liquid crystals are sealed between two glass sheets. When the distribution of liquid crystals in the LCD cell is non-uniform, defects such as active unfilled area (AUA) defects, electrostatic defects, or butterfly spots may be generated.
When laser repair is carried out to treat pixel defects such as thin film transistor (TFT) defects, bubbles may be formed at damaged areas. That is, bubble spots may be formed.
Such defects are also referred to as “heat treatment defects” in that, when defective products are subjected to heat treatment to obtain a more uniform distribution of liquid crystals in damaged areas, a certain part of the defective products remain uncured.
In order to reduce or eliminate the above-mentioned defects, dry-type heat treatment is mainly used as an LCD process for the LCD cell stage.
Liquid crystals, which have an intermediate phase between a solid phase and a liquid phase at normal temperature, are changed to have the liquid phase upon being heated to a relatively high temperature of 75° C. or more. Accordingly, when the liquid crystal is heated at a relatively high temperature, the liquid crystals may move smoothly.
In the dry-type heat treatment, LCD cells are heated in a chamber in which the LCD cells are stacked in trays, using cassettes each containing a plurality of LCD cells. Normally, the LCD cells are heated for about 120 minutes in each heat treatment. Liquid crystals, which are activated into a liquid phase in accordance with the heat treatment, exhibit a more uniform distribution as time passes. As a result, spot defects, which have been visually noticeable, disappear gradually.
In an LCD post-process carried out after an LCD drive module has been mounted, it may be possible to increase mobility of liquid crystals by driving an LCD pattern, along with the dry-type heat treatment. However, in an LCD pre-process carried out in the LCD cell stage, only a method of simply heating LCD cells is used to increase mobility of liquid crystals because the LCD drive module has not yet been mounted.
In the dry heat treatment, air is used as a heat transfer medium. Transfer of heat through a heat transfer medium is achieved in accordance with collision of molecules in the heat transfer medium. When gas such as air is used as a heat transfer medium, thermal conductivity is relatively low because the distance between molecules of gas, namely, air, is relatively long, and thus the number of times that one molecule, to which heat has been transferred, collides with another molecule is relatively small.
As a result, the time taken for liquid crystals in LCD cells to reach a target temperature is relatively long.
Furthermore, there is no method other than the heating method, as a method to promote diffusion of liquid crystals in LCD cells. Accordingly, it may be difficult to effectively achieve a more uniform distribution of liquid crystals within a relatively short time.
Because of the relatively long time for heat treatment of the LCD cells, it is difficult to achieve a uniform distribution of liquid crystals within a given time. Accordingly, spot defects of LCD cells may not be completely removed.
Consequently, quality degradation and an increase in process cost may occur and productivity may be greatly reduced.